Sealing rings are not circular in the free, uninstalled state. They have a sinusoidal shape that must be obtained with non-standard means. The shape has been previously obtained with mechanical cams, heat shaping, and other more expensive and laborious methods.
Previously, sealing rings have been manufactured from individual castings that were cast slightly larger than the finished ring. Various methods were then used to bring the ring to its final shape. All of these methods use size-specific tooling and materials that are fairly expensive. The casting method also involves fairly lengthy setups on machinery, and also requires multiple machining operations for the outside diameter and the inside diameter. This process has been used for both large and small quantities of rings.
Another method widely used is the cold "tube process". This process involves a tube of material that is usually between three inches and twenty-four inches long. The tube is cast to outer diameter and inner diameter dimensions that have an amount of material that can be machined away to leave nearly finished dimensions for the completed rings. The tube is then parted or cut into individual rings. The individual rings must still have further machining done to them to achieve the final shape. This process is actually more expensive than the individual casting method previously described, but has the advantage of using readily available tubing, as opposed to having to tool a foundry for individual castings. Another disadvantage is that it is difficult to fixture or "chuck" a tube without deforming it, thus effecting the final shape. It is more suited for small quantities of rings.
A further process that has been documented is a modified version of the "tube process", as set forth in U.S. Pat. No. 5,085,109 issued Feb. 4, 1992. In this operation, the sealing rings are machined from tubing, but the machining is done in a non-circular method and machines the final ring shape immediately from the tube without requiring a secondary machining operation for the final outer diameter and inner diameter shape. The final contour is regulated by a computer control that has the correct cross-sectional shape of the ring programmed into it. This process has been further improved in U.S. Pat. No. 5,313,694 issued May 24, 1994.
Despite the attempts of the prior art, there remains a need to manufacture sealing rings in a manner which will utilize less expensive material, significantly reduced tooling and set-up costs, eliminate casting and tubing procedures, and possess the versatility to produce rings of various sizes.